Immunologic privilege and prohibition of cellular proliferation differentiate the anterior chamber from the skin. Teleologically, both properties appear to be vital to the anatomic and functional integrity of the eye. The aqueous humor circulates through the anterior segment and is in contact with most of the structures within the anterior chamber. We and others have demonstrated that the aqueous humor contains at least one factor capable of inhibiting proliferation of lymphocytes and other non- immunologic cell types. We hypothesize that this antiproliferative activity is mediated via a biochemically identifiable molecule that functions as an important regulator of the ocular immune response and anterior segment cellular proliferation. Within this proposal we suggest three separate but inter-related projects related to the characterization of the biochemical and functional properties of this molecule. Our specific aims are: 1) to biochemically identify the antiproliferative molecule within the aqueous humor; 2) to analyze its contribution to the immune privilege of the eye, specifically to determine its capability to diminish the expression of delayed-type hypersensitivity with the AC; 3) to examine the ability of this molecule to regulate the proliferation of other non-immunologic cells important to the structural and functional integrity of the anterior segment.